Fractionator control



CONDENSER Jan. 25, 1944. A J. E. sToRM'ENT 2,340,026l

FRACTIONATR CONTROL Filed Feb. 2s. 1942 REFLUX RUN STORAGE aolvNoliovad coN oENsl-:R

INVENTOR Jost-:PH EDGAR sTo M m ATTO YS Patented Jan. 25, 1944 FRACTIONATOR CONTROL Joseph E. Storment, Bartlesville, .O kIa., as signor to Phillips Petroleum Company, acorporation of Delaware Application February 23, 1942, serial No. 432,094

" 1 Claim. (Cl. 19e-141)"l 'I This invention relatesto a method and apparatus for the control of the endpoint of distillates produced by fractionation, and more particularly it relates to a method and apparatus for thecontinuous control of the endpoint of overhead distillates produced by fractionation, and independent of the fractionating tower temperature and pressure.

It is well known that petroleum oils consist of Ymixtures of many hydrocarbon compounds some of whose boiling points lie very close together. Those compounds having similar boiling points ordinarily have similar vapor pressures, and in case a petroleum oil, or fraction or product thereof contains hydrocarbons having similar boiling 'points in about the same proportions, the partial pressures of these compounds will likewise be similar. Due to the effect of partial pressures it is dimcult to separate the different products or fractions, each containing a number of different hydrocarbons, from each other by distillation,

sincea small part of the hydrocarbons whose boiling points are higher than the temperature of distillation, usually distil over with the lighter hydrocarbons, while a small part of the lighter material remains in the heavier residue. It is `important that this overlapping of fractions be reduced to a minimum since the market value of a product isv affected by the presence therein yof hydrocarbons', lighter or heavier than those belonging in such fraction. For thisreason a close control is kept on the fractionator products and this is ordinarily done by determining the boiling range, or initial boiling points and endpoints of test samples in the laboratory at one or two hour intervals. If these tests show that the cut between adjacent fractions is not Suniciently sharp, operating temperatures and/or pressures are accordingly altered in an attempt to obtain closer fractionation. In View ofthe time consumed in sampling-a product and carrying out the distillation test, there is a considerable time lag in this method of intermittent control and it is one object of my invention to devise apparatus and amethod for continuously controlling the endpoint of volatileoverhead distillates produced by fractionation.

Another object of this invention is to furnish a method for the continuous control of the endpoint of volatile overhead distillates by the continuous control of liquid reflux independent of the top tower temperature and pressure.

Still another object of this invention is to furnish a practical and operable method for the continuous control of the endpoint of volatile overhead distillates lby Vthe continuous control of liquid reflux independent of top towertemperature and pressure and with essentiallyl no time lag in the operation.

Still other objects and advantages vwill be vapparent to those skilled in the art from a careful study of the following disclosure.

By the useof my systemof control such variables of operation as changing ratios of fixed gas to feed, etc., are eliminated from the control system. At the present time reflux vto a fractionating column may be controlled by either' the top tower temperature or the pressure, or both. Thus when changing quantities of fixed gas or other tower variables are encountered, a sample of the overhead stream being controlled, has to be sent to the control laboratory for analysis with a subsequent time lag before operations can be altered and lined out again. My means oi control tends to reduce this upsetting of tower' operation.

The figure is a diagrammatic representation of an apparatus designed for use in practicing my invention.

v The apparatus as herein disclosed consists essentially of a small accumulator I, a small flash chamber 2, a now controller 3 the operation of Y which is controlled by the temperature rneasur:

ing device 5, and heaters 4 and 6. Such auxiliary equipment as valves, etc., for purposes of sim'- plicity, have not been'shown, as Well as such other' apparatus as a still for use in connection with the fracticnator l.' y

In the operation of the apparatus according to my invention, overhead vapors from the tower l pass through line 8, condenser 9, and the condensate therefrom passes into the reiiux run storage tank lll. A small portion of this condensate stream bypasses the said run storage tank I0 and enters the small accumulator i. The amount of condensate entering this accumulator is controlled by valve ll and in normal operation this amount is small as compared tothe portion of the stream passing to the reflux storage. Excess xed gas is flashed from the small amount of condensate entering the accumulator through gas line l2. The botto'rn's'or-liquid remain-ing in this accumulator is transferred at a definite and uniform rate into the chamber 2, and this rate is controlled by pump I3. Sufficient heat is supplied by heater 4 to cause complete vaporization of this small stream so that all vapor and essentially no liquid enters flash chamber 2. The heating element 6 is used to keep the temperature on the bottom of said chamber 2 sunicently high to prevent condensation at that point, and to supply suflicient heat to compensate for heat lost through the walls in the upper section of this chamber. The temperature and the amount of heat coming from this heater 6 are such as to allow condensation in the upper section of the chamber in order to assure that the vapors will not be superheated as they pass the temperature measuring device such as thermocouple and yet prevent liquid condensate fromir'eaching the chamber bottom and accumulating therein, or in other words, this heater maintains the vapors passing through said flash chamber in a heat saturated condition. Y e

By operating this flash chamber 2 in the above described manner so that the vapors incoming through heater 4 are maintained in the vapor Applicant does not Wish to limit his invention to the use of the condensed overhead product as the reflux material -added back to the tower since numerous materials may be used for this purpose. In addition, the reuxing may be of the open or Wet trim type in which overhead product, side stream or even Water in relatively small quantities may be added directly to the top of the fractionating tower and the cooling effect of this reflux addition causes'condensation of the higher boiling vapors and therefore controls the y f end point of the eluent overhead vapors.

state and with no superheat,these vapors then passing thermocouple 5 are saturated vapors" and their temperature is correlated to the end point of the distillate being controlled. As the temperature of these .saturated vapors increases above a predetermined temperature the control mechanism I4 operates to open 4flow control valve 3 thereby permitting more reflux under pressure from pump I6 to enter the tower 1. When the temperature of theLsaid saturated vapors decreases below a given temperature, the control mechanism I4 causes controller valve 3 to close partially, thereby decreasing the amount of reflux entering saidtower, this decrease resulting in an increase in endpoint of the overhead stream.

The vapors from the flash chamber 2 issuing through line I5 may be condensed and disposed of as desired. The pressure in this flash chamber 2 is held constant by either automatic or manual control, the actual pressure maintained thereon being more or less immaterial.

The heaters 4 and 6 may be steam heaters, or electrical heaters, as desired but I have found lelectrical heaters to give excellent results dueto their ease of control. Y A l Y The control apparatus, that is, thermocouple 5, regulating device I4, and flow controller 3, may well be pieces of standard equipment of conventional and well known design.

In the operation of my process, the regulation .of the flow of reflux may be manual or automatic,

as desired, if automatic 5 isa thermocouple, I4

`is an automatic thermos-control device such that upon increase or decrease in temperature of the heat saturated vapors in the ashrchamber 2 as measured by the thermocouple 5, the opening of the flow controller valve 3 is increased or decreased which change increases orbdecreases the Aiiow of refiuxing agent into the fractionator.

The regulating device kI4 may be recording or not, as desired. A

YIf it is desired to .control the flow of reflux manually, then numeral I4 represents aV continuous temperature recording device. As this device then records temperatures, the operator may observe temperature changes vand adjust controller valve 3 to increase or decrease the flow of reflux into the towervas desired, in which case 3 is just an ordinary valve.

,. addition is decreased.

in the top of the fractionating tower in order to control the end point of the vapors passing over said coils and from the tower as overhead product. Water, condensed and cooled overhead product or other product stream may be circulated through these closed vcoils for reiiuxing purposes in whichroperation the amount of reflux circulated is controlled by the temperature of the heat saturatedvapors passing the herein described flash chamberZ, and bysuch control the endpoint of the overhead vapor stream is controlled. Y

In some cases it may be desirable to employ wet trim and dry trim reiluxing simultaneously in an eiort to control overhead endpoints more efliciently, and in such cases this combined or double reiluxing is intended to be included Within the scope of applicants invention as herein disclosed.

Applicant does not wish to limit his invention to the one fulLv discussed embodiment since the several types of refluxing, and other alterations and variations obvious to those skilled in the art come within the intended scope of my invention.

What I claim is;V s

In the fractionation of volatile hydrocarbon mixtures in which the fractionator is refiuxed, a method for controlling the end point of the fractionator overhead product substantially independent of varying quantities of iixed gases Vcomprising condensing at least a portion of the overhead from saidgbfractionator, removing excess xed gases from` the liquid condensate, vaporizing the liquid condensate and passing the vapors through a flash Y, chamber, heating the lower portion of said flash chanrber sufliciently high to prevent condensation of liquid at the bottom but regulating the temperature and amount of heat toallow` condensation in the upper portion of said chamber, thereby maintaining the vapors in a heatV saturated condition ,while passing through saidflrash chamber, and

measuring the temperature of the heat saturated vapors and controlling thel amount of reflux added to therfractionator by any changes in ,temperature of the heat saturated vapors, wherefin upon increase of the temperature of the said vheat saturated vapors, theu reflux addition is in creased, and upon decrease of the temperature of the said heat saturated vapors, the redux 

